Minimizing vibrations of turbine blading is important to minimize blade failure problems.
This invention relates to turbine blading. In particular, the invention is concerned with blading for steam turbines.
Blading for steam turbines have been constructed in many formats. Short grouped blading is provided where tips of neighboring blades are connected to form packets of approximately 3 to 12 blades in a group. To overcome vibration problems with such blading, techniques such as long-arc harmonic, double harmonic or continuous harmonic shrouding are developed from existing grouped bladings.
An alternative approach to avoiding vibration problems is the provision of an integral covered blading. In such a system, each blade is formed integrally at initial fabrication with its own cover. The blading is then located on the rotor of a turbine in its designed position. Blading assembled in this manner minimize lower and high frequency modes excited by the running speed of the rotor or a nozzle wake frequency.
In practice, turbines have a long life and blading currently in use in many turbines are of the grouped short arc design. When blade failure problems are encountered, it is necessary to replace the blading with some other design in order to return the turbine to service quickly. Such blade replacement is relatively expensive and results in wastage since many of the blades in the turbine are still in good condition.
It is an object of the present invention to provide a method and product for providing integral cover blades for a turbine which is different to the known integral cover blades and which can provide advantages over other blade cover techniques.